The invention relates to a process for obtaining lithium-based thin sheets and its application to the production of negative plates for accumulators.
A person skilled in the art knows that lithium is a metal which, in addition to very high reactivity with damp air, has very poor mechanical properties and has a marked tendency to adhere to the majority of materials. These are all factors which make it difficult to obtain thin sheets of lithium by rolling, particularly if thicknesses of less than 200 .mu.m are to be obtained. They can obviously be obtained by taking the precaution of working in an air atmosphere having a low moisture content or in a noble gas atmosphere, of multiplying the rolling passes and using non-stick devices during rolling and/or winding, but the transformation costs are therefore too high for certain potential applications of this material such as, for example, the production of negative plates provided in certain accumulators containing organic electrolyte.
It is therefore worthwhile and necessary to have suitable means for solving this problem of rollability of the lithium.
Solutions have obviously already been recommended. Thus, for example, in Russian author's certificate no. 1103912 there is described a process for rolling lithium involving rolling the lithium by means of cylinders cooled to a temperature below 0.degree. C. which is characterised in that, to prevent adhesion of the lithium to the cylinders during rolling and to improve the quality of the sheets obtained, rolling is carried out under inert gas which has been dried to a dew point below the temperature of the working surface of the cylinders; the temperature of the working surface of the cylinders being maintained between -1.degree. and -100.degree. C. by introduction of a coolant (liquid nitrogen in this instance) into the internal cavity of the cylinders. The lower the desired thickness for the sheet, the lower the temperature of the working surface. Thus, it is -30.degree. C. for a 100 .mu.m sheet and -100.degree. C. for 70 .mu.m.
Furthermore, it is also mentioned in this document that the lithium can be rolled between cylinders produced from a polymeric material.
The two solutions proposed involve technological improvements relating to the rolling process itself and necessitate either special arrangements such as introduction of liquefied gas into the interior of the cylinders or cylinders of special material.